PUNDITS, journalists, campaign hands and others spend an awesome amount of time during election season trying to work out what factors will swing the vote one way or another. Could it be a candidate’s likeability? Differences in policy? Her ad strategy? His habit of insulting large swathes of the electorate?
Campaign choices matter, but political science research suggests that the lay of the electoral land is largely shaped by factors beyond candidates’ control. People vote retrospectively, based on their perception of how things are going for them and those around them. But their perceptions are shaped by all sorts of things. As Christopher Achen, of Princeton University, and Larry Bartels, of Vanderbilt University, describe in Democracy for Realists, a book published earlier this year, voters sometimes punish politicians for bad weather, random misfortunes—an outbreak of shark attacks appears to have cost Woodrow Wilson votes in the 1916 election—and the performance of the local American football team.
Perhaps more importantly, voters are extremely myopic. They care about their economic welfare, and especially about whether or not their incomes are growing. In making this judgment, however, the months immediately prior to the election are critical. Messrs Achen and Bartels reckon that few variables matter anywhere near as much as growth in disposable personal income, adjusted for inflation, in the six months prior to election day. Indeed, they note, just two variables—short-run income growth and the tenure of the incumbent party—represent the most reliable predictors of the incumbent party’s vote share (see chart). Those measures predict a close race in 2016. Indeed, a closely watched election model put together by Ray Fair, of Yale University, based on economic fundamentals, predicts a Republican victory in November. While real income growth is running at a respectable 1.4% annual rate, Democrats have held office for the last eight years and the popular incumbent president is not himself on the ballot.
Polling, of course, increasingly points to a Democratic victory, and probably a resounding one. This divergence is down to the fact that short-run economic growth and tenure are not everything; other factors—like wars, social unrest, or the presence on the ballot of an historically inept and divisive candidate—also matter. But should Mrs Clinton win on November 8th, this surprisingly effective model of electoral performance suggests the road to re-election will be a difficult one indeed. It would take growth in real disposable income of greater than 2% in the months before the 2020 election to counteract the effect of 12 years of Democratic incumbency. The road to a second term will be smoother if Republicans again nominate a poor candidate. If Mrs Clinton hopes to beat a garden variety Republican in 2020, she had better be thinking hard about how to get Americans’ real incomes growing rapidly by the end of her first term.